I found this image on the internet, I dont have the source at hand it so it could be fan art, I haven't looked deeply enough into it. It suggests the use of contra fiel generators to reduce apparent mass of macro shells (after they leave the ship) so they can achieve the multi-thousand km/speedshttp://imageshack.us/photo/my-images/81 ... hefirs.png

Thats art done by Magelord, he did some stuff for the Anargo sector project, which is more or less in stasis at the moment IIRC.

I've had his atmospheric Fury as my desktop on and off for ages. His art is fucking awesome, but its not in any way official as I understand it.

He's also the guy who did the ships on that size comparison chart website IIRC.

As a rule of thumb I've been going more along the lines of thousands/tens of thousands of km/s, that leads to some not so insane propellant requirements, and it can kind of be justified based on estimated plasma cannon velocities (starship or ground based.)

noted

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If you stick with thinner hull thicknesses (EG 5 meters as per Emperor's Mercy) then it probably won't be nearly that massive. And then there's always hull densities (what if the density of the magic metals is closer to aluminum or titanium rather than iron or tungsten?)

noted

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pace fleet indicated 'conventional nuclear fuels' as I recall it, which can mean anything from fission to antimatter. It also doesn't specify the efficiencies of the reaction (not all fusion reactions are alike as I recall on atomic rockets) so its open for debate. Not to mention the not-so-minor probelm of explaining how one kg of fuel can break E=MC^2

The energy density of fusion i used was 6.3×10^14 one two orders of magnitude lower than anti-matter/matter annihilation (with the plasma somewhere between the two)

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That depends on how you defined the exact quantity of fuel the Goliath carries.

RT and spacefleet claim 'several million tons' - 'millions of tons'

ill post the 3 gigaton ting if i find it incase anyone wants it - it was similar to the 112 5 gigaton warheads, only using megaton warheads instead amounting to 3 gigatons.

thanks for the feedback its most use full nd educational I am going to go refine/diversify (differeing masses/propellant velocities etc.) my workings a little taking these things into account

The energy density of fusion i used was 6.3×10^14 one two orders of magnitude lower than anti-matter/matter annihilation (with the plasma somewhere between the two)

1000x fusion is going to be 6e17 J per kg, which is far higher than the 9e16J approximate of one kg of matter converted completely to energy. If you used antimatter as the baselines (conventional nuclear fuesl can apply to alot of things) is 9e19 J per kg.

If you used fissionable fuels you get roughly in the benchmark of 100% matter-to-energy conversion, which fits with certain other depictions of 'plasma' (EG plasma grenades as per Wargear, etc.)

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RT and spacefleet claim 'several million tons' - 'millions of tons'

YEah, but the problem there is that if you only assume 2-3 millions, then you hit that 'violate E=MC^2' problem again. IIRC its around 3-4e27 J to remove the Earth's atmosphere. That's 2-3e9 kg.. which is 1e18-2e18 J per kg. If you get something approaching a hundred million or a billion tons, you get around e15-e16 J per kg, which is less problematic.

There is still that whole 'is it an earthlike atmosphere or not' which is going to be a point of contention people are bound to argue over, though.

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ill post the 3 gigaton ting if i find it incase anyone wants it - it was similar to the 112 5 gigaton warheads, only using megaton warheads instead amounting to 3 gigatons.

Well if you find it I'll be interested to see it. I really don't see much point establishing specific benchmarks, because as my own analysis demonstrates things can pop up to change the dynamic every once in awhile. I used to argue thousands of gees was standar,d then came along Rogue Trader. And there's always different cases with the novels. Ship scaling and masses run on similar 'interesting' problems (although Titans are worse off here...)

We know that Macro cannon shells are often described as being roughly the size of a tank (which we might figure between 30-60 tons for IG tanks as a baselines) We also know in real life that nuclear yield-to-weight ratios range somehwere between 1-5 megatons per ton of mass. So assuming a macro cannon shell was no better technologically than modern nukes (which are mostly fission IIRC) you get between 30-300 megatons per shell. With dozens or hundreds you're getting into single or double digit GT broadsides.

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thanks for the feedback its most use full nd educational I am going to go refine/diversify (differeing masses/propellant velocities etc.) my workings a little taking these things into account

In my experience you don't want to try to narrow things down too much, unless you don't have a problem admitting you're wrong later on, because the chances are good that something will come along to say you are. I used to argue hundreds ro thousands of gees as standard, and those have dropped easily by an order of magntiude or more since Rogue Trader came out. I also used to think teraton/petaton range firepower for 40K starships, but that's slipped downwards some as well (probably was silly to think all ships packed that much firepower as standard to begin with.)

It also doesn't hurt to acknowledge that the scale can be alot wider than where one believes the 'actual' range exists. 15 tetrajoule las broadsides or 'kiloton' macro cannons won't go away any more than the near-c nova cannon/quarter-c bombardment cannon will.

Regarding size ranges- one thing that occurs to me is that some cruisers may be much boxier, with a higher width-to-length ratio than others. For example, some of the big 'cruisers' have those big nova cannon: those sound like long-barreled axial weapons, and you may need a long, spindly hull to build the nova gun into the keel of the ship. The long narrow hull also favors bow-on engagements, because it means you present a much smaller target to the enemy. And you can save mass on your main armor belt by putting it perpendicular to the axis of the ship, like the gun shield on an artillery piece.

(It doesn't have to stick out like a gun shield, it can just be a solid "pie plate" of armor that separates the expendable stuff near the front end of the ship from the important stuff near the back, built into the hull where you can't easily see it).

Whereas something designed to launch broadside barrages of torpedo and what Battlefleet: Gothic models as "weapons" or "lance" fire might well be built shorter but with a fatter hull, so that it can wrap more defensive depth of armor and shielding and expendable spaces (like crew quarters and fuel bunkers) around the core hull.

Possibly. We know that the Essene from Eisenhorn was 3 km long and 700 m tall (which was basically as large as older cruisers) whilst the FFG cruisers were 5 km long and .8 km at the fins, so there is reason to believe that 'length to width/height' ratios vary. Given that engines and prows (or lack of prows) has been a significant contriubtor to lenght (engines make up something like 1/3 to 1/2 the length/mass of a ship, depending on source, so putting in a different engine system would adjust the dimensions of the ship.)

Fudge it a bit further by differences in technology, consturction, etc. from sector to sector/planet to planet to permit individual differences in design and that might account for most differences.

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This actually makes a lot of sense if life support and routine sensor watch use less energy than firing up the main engine. We normally think of high-power SF drives as being continuous boost, but there's no logical reason to do that if it doesn't pay.

For a continuous-boost spaceship with high accelerations, adding an extra hour of engine burn time gives you diminishing returns in saved travel time. The first hour gives you a fixed travel time, say 60 days. The second hour gives you a travel time of 30 days (one half that). The third gives you 20 days (one third), and so on.

It might not, under a variety of conditions. Say, if you aren't confident of being able to refuel and your tanks are low. Or if you might have to fight a very energetic and dangerous battle at the end of your mission. Or if this is a routine redeployment of troops or ships and you aren't in any real hurry to get things done. Or you aren't totally sure of how long your century-old most Omnissiah-blessed rocket engines will hold up under a continuous 50g burn and don't want to risk blowing a gasket before your next scheduled maintenance stop.

So maybe 120 hours in transit is a smarter option than spending 1 hour burning the engines at top acceleration. Unless you're in a hurry.

Could be. again I probably wouldn't generalize as I'm sure there are some contradictory examples. Given the variation of technology (STC standardization only goes so far) we could envision a variety of engines with different performance criteria for givne hulls. Rogue Trader (The RPG) tends to go this route with their ship design and constriction, and we also know of Battlecruisers in BFG (which were cruiser hulls with IIRC battleship engines strapped on) an the Voss-pattern vessels (which were light cruisers that had shitty engine performance, but could compensate with firepower and I think durability.)

One of the things tht has sort of been glossed over in more recent editions is whether or not 40K ships carry onboard workshop/fabrication facilities. In Space Fleet, all ships had them to build the stuff they needed to repair and maintain it in the field, but as warp speeds have gone up (since BFG era) the transit times and times 'away from base' seem to have gone down (months instead of decades.) the BFG rules mention that there are workshops onboard for building/reparing fighters but that's it. and FFG's Rogue trader stuff implies that more ships (at least in Calixis) get my on stores.

In all probability its handled on a sector by sector basis, with battlefleets customized to the roles and enviroment they operate in. That means some fleets might be designed for long-range, independent operation (which can have implications for their invidiual capabilities including engine performance) whilst others might be designed to return to base more often (weeks or months away from base.)

Crew complements are another area where 'variation' exists.. cruisers and battleships carried thousands or tens of thousands per ship (and escorts I think hundreds) earlier on, but thats gone to tens or hundreds of thousands average with FFG material.

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Of course, there's a great difference between sustained barrage and individual weapon capability.

At the Somme, the British fired off roughly one and three quarter million artillery shells, easily translating to a few thousand tons of explosives. This does not mean they managed to do as much damage to the German lines as a couple of low-yield tactical nuclear warheads would have done.

The same comparison might lend itself to a seven-day bombardment from shipboard energy weapons, versus a few shots from something like a nova cannon.

That's one inteprretation, although we're probably talking minutes worth of bombardment (less than an hour) rather than days. On the other hand some sources have indicated that ship to ship encounters are mostly manuvering for position and to make single, brief broadside passes. In that context a turn could be mostly moving about for advantage, followed by very brief barrages being fired. Or maybe multiple barrages.

Some people I have known believe that macro cannon shells take upwards of half an hour to hit the target across tens or hundreds of thousands of km. I haven't figured out how that's supposed to be (with unguided shells.) either.

I was the letter-writer in question. If the densities were in line with modern naval vessels, they'd be between 50 and 100 times the listed masses. However, the official word, insofar as there is such a thing in 40k, is that the materials used are extremely light and strong. There was no reference to "mass-lightening" in the return letter I received; that's just a Star Trek thing.

So, yes. The ship is made of aerogel. Nuke-proof aerogel. You can bring that up to the next person who claims that 40k vessels are crude and cumbersome.

How much the ship masses doesn't really have any effect on how cumbersome it would be, that's more an issue of thrust to weight ratio and how well they can vector said thrust. Modern spacecraft are the most advanced products humanity can make in terms of manufactured goods but remain immensely cumbersome and performance limited for example.

"This cult of special forces is as sensible as to form a Royal Corps of Tree Climbers and say that no soldier who does not wear its green hat with a bunch of oak leaves stuck in it should be expected to climb a tree"— Field Marshal William Slim 1956

I was the letter-writer in question. If the densities were in line with modern naval vessels, they'd be between 50 and 100 times the listed masses. However, the official word, insofar as there is such a thing in 40k, is that the materials used are extremely light and strong. There was no reference to "mass-lightening" in the return letter I received; that's just a Star Trek thing.

So, yes. The ship is made of aerogel. Nuke-proof aerogel. You can bring that up to the next person who claims that 40k vessels are crude and cumbersome.

Are you estimating 'average density' - eg the mass of the ship divided by its estimated internal volume, or are the density estimates based on 'overall volume minus the empty space air volume estimated' which would require knowing, amongst other things, hull thickness (as well as other thicknesses between compartments, etc.) Because doing the mass calcs the "easy" way actually result in masses not dramatically off (eg within an order of magnitude) of what the FFG stuff actually says, at least for escorts. Using the Cobra or the Sword as a baseline (and making allowances for the fact that there's alot of empty space and spindly bits on both ship, plus all those fins and lil pointy bits sticking out in random spots) I usually got an average density around 150-200 kg*m^3, which is about what Atomic Rockets estimates as possible (albeit on the low end.) and as I noted it matches up reasonably well with what the honorverse uses for the 'resized' naval ships, so I take that as proof it probably isn't implausible.

Moreover, even if we go with something more dense (say a battleship for some reason) the figure is not going to be off by more than a few times if that, and that's still within a definition of 'approximate' - its not as if this is somehow LESS precise than most sci fi calcs.

The one caveat to this is that the mass figures work better for escorts than they do with the capital ships, as cruisers and such tend to be larger and blockier (I got average density figures for cruisers about half that for escorts) Funny thing is if the cruiser sizes had stuck with the 3-4 km sizes from other novels (but not the 8 km.. lets not go there now) it actually didn't have this problem.

well I dont have the models so I can't do exact measurements, but I remember using pics I grabbed off the net on various angles and figuring that the width of the Cobra's hull minus fins is something like 120 m or so. It's quite a bit taller (depending on the point you measure, its around 200-240 m depending on where you measure and excluding the widest point). The main thing is with the lenght.. the engine nozzles stick quite a bit out, and the front prow slopes a bit, so that can exaggerate volume somewhere too.. I figure the prow is maybe 250 m or so long, and the bulk of the ship (minus rear thrusters) is around 1200m or so. I get around 33-40 million cubic metres for volume based on those estimations. That yielded about the 150-172 kg*m^3 density, but the actual ranges IIRC could yield lower volumes depending on the exact measurements you went with.

That's one reason I really carp on the whole 'approximate' thing, the measuremnts aren't ever going to be exact, and its likely the mass isn't going to be either, but even you went with say .6 tons per cubic metre as a density you're getting 'only' 24 million tons for a Cobra, which is not exactly a massive difference (as far as sci fi calcs go - order of magnitude and that) from the RT numbers.

Cruisers, as I said, are a bit of a different story. 800 m wide (at fins IIRC) and prboably about that tall, and 5 km long.. Its really hard to get average densities because a Lunar is not a solid block either (one of my more flawed assumptions with past calcs - I never really looked at them from top down!) but even with fairly generous assumptions about volume (4 km 'actual' length, ignoring stuff sticking out at vraious points, 200 m 'wide' ignoring fins, and 500 m 'tall' ignoring sticking bits out again) you only get something like 70 kg*m^3 density, and it can get much worse with lower end figures. Again its not a.. huge difference, and if the lengths were shorter I think it wouldn't be as huge a problem for the givne masses, but there ya go.

It's not exactly unprecedented either.. millions/tens of millions of tons has shown up in novels prior to RT when it came to ship masses, so I dont know if they knew about those or just made up their own numbers. The worst you could accuse them of was ignoring the previously established lengths for cruisers (3-4 km long) but thats probably about it.

I have found the 2 gigaton torpedo, it is in fact a warp missile that jumps in and out of the warp on its course towards its target, making it more difficult to track and target for enemy defenses, the missile is also described as "gigantic" and is fired from a Battle Barge. The actual warheads are far more ordinary than its warp delivery system. The quote comes from the Horus Heresy book: Age of Darkness.

"The torpedo-generated image image swirled into static for a few seconds as the missiles separated, each disgorging four hundred warheads at the Salamanders cruiser. When the relay returned the view was filled with a cloud of sixteen hundred glimmering projectiles. Explosions blotted out the stars as the Salamanders craft swooped climbed and rolled through the mass, blasting away with cannons and lasers. As the warhead launchers continued to power towards the strike cruiser - each containing a five megatonne nuclear charge - the defense turrets of the Salamanders vessel opened up."

The book goes on to describe the effect of these warheads on the light cruiser: "Blue and purple lighting flickered as the remaining warheads, several hundred of them, slammed into the strike cruiser's shields. The vessel was engulfed by a blaze of detonations, so bright it appeared on the main display like a nova being born. More explosions followed as the shields overloaded and the remaining warheads struck the cruiser's armoured hull. Plasma billowed from a ruptured engine duct. A moment later the mini-screen vanished as the warhead launchers detonated. 'Scanners confirm severe engine damage and moderate damage to the starboard gunnery decks.'

Its interesting that these torpedoes interacted with the shields - maybe they had quite some speed compared to ordinary or at least more common/mainstream torpedoes which one source gives speeds of tens-of-km/second for (believe some evidence leads to hundreds km/s?). So maybe hundreds to a few thousand km/s for these? The weapons were powerful enough to cause critical damage to the engines and some 'moderate' damage to the hull its self.

The former. I would be interested in seeing your measurement estimates.

Having scanned your email exchange it looks like you used a mass of 1MT for the nimitz carrier. This is a factor of 10 too large. Thinking about it there is no way a carrier can be 50% the density of iron; 4x the density of water and still float.

Going with a carrier mass of 0.1 MT and assuming mass scales as length cubed then the 1500m long Cobra is 5x the length and so 125x the mass, so in the 10MT range, which is actually not far off the 5MT figure floating around.

'Next time I let Superman take charge, just hit me. Real hard.''You're a princess from a society of immortal warriors. I'm a rich kids with issues. Lots of issues.''No. No dating for the Batman. It might cut into your brooding time.''Tactically we have multiple objectives. So we need to split into teams.'-'Dibs on the Amazon!''Hey, we both have a Martian's phone number on our speed dial. I think I deserve the benefit of the doubt.''You know, for a guy with like 50 different kinds of vision, you sure are blind.'

The former. I would be interested in seeing your measurement estimates.

Having scanned your email exchange it looks like you used a mass of 1MT for the nimitz carrier. This is a factor of 10 too large. Thinking about it there is no way a carrier can be 50% the density of iron; 4x the density of water and still float.

Going with a carrier mass of 0.1 MT and assuming mass scales as length cubed then the 1500m long Cobra is 5x the length and so 125x the mass, so in the 10MT range, which is actually not far off the 5MT figure floating around.

oddly this doesn't quite seem to hold up well when I do it with cruisers. 5000 m long and 800 m wide (IIRC) means that a cruiser should be ~24x more massive than a 1500 m long, 300m wide cruiser (I got something like 1620x a difference in volume comparing the cruiser to an aircraft carrier, which is some 162 million tons, and a Lunar is listed as only 28 million...)

Funny enough, if I use the 3 km long, 700 m wide cruiser estimate similar to the Essene (from the Eisenhorn series) I 'only' get 75 million tonnes or so, which is much closer.to the stated approximate mass (If I use the length/wdith ratios for the Lunar and scale it to a 3 km long cruiser, I get ~480m width, and a ratio of 'only' 350, which yields a mass aruond 35 million tons.)

I have found the 2 gigaton torpedo, it is in fact a warp missile that jumps in and out of the warp on its course towards its target, making it more difficult to track and target for enemy defenses, the missile is also described as "gigantic" and is fired from a Battle Barge. The actual warheads are far more ordinary than its warp delivery system. The quote comes from the Horus Heresy book: Age of Darkness.

"The torpedo-generated image image swirled into static for a few seconds as the missiles separated, each disgorging four hundred warheads at the Salamanders cruiser. When the relay returned the view was filled with a cloud of sixteen hundred glimmering projectiles. Explosions blotted out the stars as the Salamanders craft swooped climbed and rolled through the mass, blasting away with cannons and lasers. As the warhead launchers continued to power towards the strike cruiser - each containing a five megatonne nuclear charge - the defense turrets of the Salamanders vessel opened up."

The book goes on to describe the effect of these warheads on the light cruiser: "Blue and purple lighting flickered as the remaining warheads, several hundred of them, slammed into the strike cruiser's shields. The vessel was engulfed by a blaze of detonations, so bright it appeared on the main display like a nova being born. More explosions followed as the shields overloaded and the remaining warheads struck the cruiser's armoured hull. Plasma billowed from a ruptured engine duct. A moment later the mini-screen vanished as the warhead launchers detonated. 'Scanners confirm severe engine damage and moderate damage to the starboard gunnery decks.'

Its interesting that these torpedoes interacted with the shields - maybe they had quite some speed compared to ordinary or at least more common/mainstream torpedoes which one source gives speeds of tens-of-km/second for (believe some evidence leads to hundreds km/s?). So maybe hundreds to a few thousand km/s for these? The weapons were powerful enough to cause critical damage to the engines and some 'moderate' damage to the hull its self.

I remember that passage. 4 warp-torpedoes, which were basically like the old warp missiles from the old Titan wargames (basically the missiles made a hop through the warp, bypassed shields, and struck the titan directly.) Which was all well and good except for the fact the warpedoes were basically fired at far less than a light second (so they really weren't moving much faster than regular torpedoes can) and all the hopping in and out of the warp seemed pretty superfluous. Part of this is just Gav Thorpe seeming to like really really short ranges and low velocities when it comes to space stuff, so.. go figure.

Anyhow, the torpedoes each launched some 400 submunitions (another Gav Thorpe favorite for his space weaponry) and the launcher which had a '5 megatonne' charge on it. I gather you're figuring the submunitions had the same yield as the launcher. Which it might have except.. we don't really know for sure. It could be 5 megaton, or it could be 12 megaton (a warhead of that yeidl was mentioned in Deliverance Lost, but the context - whether it was a submuintion torpedo, a nova bomb, or a regular missile was not clarified.) Or it might be alot less. without the yield of the submunitions stated the value of that quote is limited.

One possibility is based on Deliverance Lost - we get mention of fairly compact, 500 kiloton mining charges IIRC (compact enough people could lift them up and carry them, and certainly a single Astartes can carry one). You might assume each submunition is at LEAST that powerful, which would be around 200 megatons (205 really) yield per torpedo. Alternately, you could base the submunitions off the James Swallow 'Atlas class' space to ground nukes, which were stated to be megaton range in the Blood Angels omnibus (the first one) and also specifically mentioned to be anti-Titan (and hardened target) weapons, so they should be far weaker than what is needed to damage a starship (going by what Drachenfels captain said in Execution Hour, at least.) Assuming at least 1 Megaton atlas class equal to a submunition, thats 405 megatons per torpedo.

I have the models - scaled them roughly and with estimated hull thicknesses for various regions of the ship (ranging from 3 meters as per 'meters thick' 20m from RT to 55m from model-prow scaling). From these estimates the outer hull and heavy armour would represent ~10% of the total cruisers volume. Using various densities from very low to very high (by modern standards) arrive at 4 estimations of mass - 200mt - 400mt - 1,600mt - 3,757mt

I remember that passage. 4 warp-torpedoes, which were basically like the old warp missiles from the old Titan wargames (basically the missiles made a hop through the warp, bypassed shields, and struck the titan directly.) Which was all well and good except for the fact the warpedoes were basically fired at far less than a light second (so they really weren't moving much faster than regular torpedoes can) and all the hopping in and out of the warp seemed pretty superfluous.

Being able to teleport past the enemy's shields sounds kind of important.

Being able to teleport past the enemy's shields sounds kind of important.

Oh it would be if they had done it here. But the torpedoes actually had to drop out of the warp for their final runs (which subjected them not only to point defense but also fighter interception), and they submunitioned to actually strike the shields before bypassing to cripple the ship itself.

I have the models - scaled them roughly and with estimated hull thicknesses for various regions of the ship (ranging from 3 meters as per 'meters thick' 20m from RT to 55m from model-prow scaling). From these estimates the outer hull and heavy armour would represent ~10% of the total cruisers volume. Using various densities from very low to very high (by modern standards) arrive at 4 estimations of mass - 200mt - 400mt - 1,600mt - 3,757mt

Um, for what vessel ? and what densities are you using? I'd guess a crusier but..

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